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This is almost the same cl as
https://chromium-review.googlesource.com/c/chromium/src/+/1226715

The previous cl was reverted because it broke linux-chromeos-dbg due to missing
"=0" for a virtual method of an abstract class (incorrect gn config meant the
compiler didn't pick it up). It's added in this cl. This is
the only change from the previous cl.

Bug: 881215
Change-Id: Iaf5ab6e3ee98c11b593dcc9d759527c4fb3b2168
Reviewed-on: https://chromium-review.googlesource.com/1235262Reviewed-by: Michael Martis <martis@chromium.org>
Commit-Queue: Jia Meng <jiameng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592698}